1Plants make their own food
Plants make their own food by photosynthesis. A leaf takes in carbon dioxide from the air and water from the roots, and uses light energy to turn them into glucose and oxygen.
photosynthesis
Lesson 19.1 notes
Making food from light
What plants need to make food, the word summary, chloroplasts and chlorophyll, what plants do with glucose, and minerals from the soil.
2The word summary
carbon dioxide + water → glucose + oxygen. Carbon dioxide and water are the reactants; glucose and oxygen are the products. Light gives the energy.
reactantsproducts
3Chloroplasts
Photosynthesis happens in chloroplasts, inside plant cells. They contain chlorophyll, a green substance that absorbs light energy. Only parts with chlorophyll, usually the green parts, photosynthesise: roots have no chloroplasts.
chloroplastchlorophyll
4Why leaves are green
Sunlight is a mix of colours. Chlorophyll absorbs red and blue light best. It absorbs less green light and reflects more of it, so leaves look green.
absorbreflect
5What plants do with glucose
Plants use some glucose for respiration, to release energy. They turn the rest into starch to store, cellulose to build cell walls, proteins to grow, and fats and oils to store in seeds.
starchcellulose
6Minerals from the soil
Roots take in water and small amounts of minerals from the soil. Plants need nitrates to make proteins and magnesium to make chlorophyll. Without them, plants grow poorly with yellow leaves.
mineralsnitrates
7Where a tree's mass comes from
In the 1600s, van Helmont grew a willow for 5 years. It gained 74 kg, but its soil lost only 57 g. We now know it was built mostly from carbon dioxide and water.
Explore: Photosynthesis lab
Switch the light, the carbon dioxide and the water on and off, and see when a leaf can make glucose and oxygen.
Common mistake: Plants make their food from carbon dioxide and water
Plants don't get their food from the soil. They make glucose from water and carbon dioxide from the air, using light energy. The soil gives them water and small amounts of minerals.
Remember
- carbon dioxide + water → glucose + oxygen. Chlorophyll in the chloroplasts absorbs the light energy that drives it.
- Plants use glucose for respiration, and to make starch (a store), cellulose (for cell walls), proteins, and fats and oils.
- Roots take in water and minerals from the soil. Plants need nitrates to make proteins and magnesium to make chlorophyll.
Going further at GCSE